Wrong bulbs installed?
Defective or corroded sockets?
Bad turn signal flasher?
WHAT YEAR ?????
Probably the switch on the lever that the brake pedal is attached to.
first check fuses then flasher unit if still no joy get out your multitester or take to the shop d.cop
Usually a bad hazard flasher module a common problem. Try playing with hazard switch.
That's probably because that's the older van and the more original blinkers
The Relay for the blinkers on a 2000 Cavalier is under the drivers side of the dash. It is mounted close to the kick panel .
Replace the turn signal flasher relay.
Most likely you have a flasher that needs to be replaced.
Check the fuse
If the fuse is good and the bulbs are good, replace the flasher relay.
I am currently having the same problem you are having check the fuse to see if it is blown the blinkers and brake lights are on the same fuse my system has a short in it somewhere and is popping the fuses I am in the process of running new wires since the wonderful people at Chevy ran all the wires thru the frame and you can't access them
You need to replace your turn signal flasher. Check with your Chevy dealer for the location when you buy it.(10.00)